Since 1910, the Smithsonian's National Museum of Natural History has inspired curiosity and learning about the natural world and our place in it.

04/28/2015

The First Sea Stars Known From Hydrothermal Vents

Paulasterias tyleri feeding on deep-sea barnacles. Image courtesy of the British Antarctic Survey.

I am Dr. Christopher Mah, a Research Collaborator in the Department of Invertebrate Zoology and my title is a descriptor of what I do! My research focuses on the diversity and evolution of sea stars, which most people are probably most familiar with as star-shaped inhabitants of beaches and intertidal zones. What most people don’t realize is that sea stars occur at all depths, some live in depths of over 8000 meters! By comparison, the deepest point of the Grand Canyon is only about 1800 meters (6000 feet). It also surprises many people that sea stars occur in environments which are very inhospitable to humans. A great diversity of sea stars can be found in the Southern Ocean (Antarctica), some living in only a few meters of water but others occur thousands of meters below the ice-covered ocean surface. So, that’s a double-whammy: Antarctic AND deep-sea!!

One of the museum’s core strengths is that of partnership, collaboration with other organizations both in the United States and abroad. It’s not unusual for some of the most important discoveries to result from collaboration with MANY other scientific institutions!

An expedition undertaken by the British Antarctic Survey (BAS) in 2012 discovered that hydrothermal vents were present at approximately 2,400 meters depth on the seafloor of the Scotia Arc region in Antarctica. These are regions where toxic chemicals, such as hydrogen sulfide, bubble out of geothermal/volcanic openings on the bottom of the ocean. Surprisingly, an array of unique animals survive and thrive in these hostile environments. Among the most surprising of discoveries from this region was an enigmatic 7-rayed sea star which biologists and geologists observed feeding on the crustaceans living amidst the hydrothermal vents!

Paulasterias tyleri (about 2 inches in diameter) has been observed feeding on the barnacles and the “hoff crabs” which also live in the vent system. P. tyleri can have 7-8 arms. Image by C.Mah.

My colleagues at the BAS contacted me in due time and sent me the specimens for study and analysis. At the same time I had just completed the 2009 Pacific Northwest expedition with the Monterey Bay Aquarium Research Institute (MBARI). We had been studying deep-sea geology and biology along the Juan de Fuca and Gorda mid-ocean ridges (adjacent to hydrothermal vents) in the deeps of the North Pacific Ocean and had just collected a mysterious new species of 6-rayed sea star which was widely present in the area, from 2200-3300 meters.

The second species discovered, Paulasterias mcclaini (about 1 inch in diameter), is named for deep-sea biologist Dr. Craig McClain at the NESCENT center at Duke University. Image by C. Mah.

Molecular analysis of these two, seemingly independent, specimens revealed a surprising result: they were closely related to one another! Additionally, they emerged on an evolutionary lineage independent of other closely related sea stars. Further work analyzing their body form, using features viewed with our scanning electron microscope (SEM), clarified the relationship between these two new species.

P. tyleri has seven arms, a very soft body wall and distinctive structures known as pedicellariae, which resemble jaws, seen in the SEM image above. Image by C. Mah & Bob Ford.

Two NEW species from very different locales at bathyal depths of the ocean: the Antarctic and the North Pacific, which analysis has further revealed to be members of a NEW family! Paulasteriidae is the new family, which includes two species: Paulasterias tyleri and Paulasterias mcclaini. This is one of the first new families to be described since 2002! Very disparate pieces of a deep-sea puzzle have been brought together by study at the museum through efforts from teams on two continents and about five different institutions! I was happy to have named the species/genus/family of these animals but I am especially grateful that so many scientists have been so cooperative and worked so hard to make such a project successful!

Comments

You can follow this conversation by subscribing to the comment feed for this post.

Hi Tracey,
The specimens were collected using a Remotely Operated Vehicle operated by the British Antarctic Survey. So, observed via video and then collected with some collection arm or other similar device. Water temp in this area was variable. "Background" was below freezing (-1.5C) whereas the vent itself was almost 400 C (380 degrees). The stars were collected in a zone intermediate, so about 9-15 degrees or so? Temps were variable.